More from WebMD

April 30, 2012 -- A pair of new studies aims to clear up some of the confusion over what age women should start getting routine mammograms to screen for breast cancer.

The studies, which are published in the Annals of Internal Medicine, show that a woman in her 40s who has extremely dense breasts, or who has a mother or sister with breast cancer, reaps the same benefits and drawbacks from getting regular mammograms as a woman in her 50s.

Researchers say that meets a "threshold of risk" that may help guide women and their doctors to start regular mammograms at age 40 instead of age 50, as some current guidelines suggest.

"They're really taking a better look and saying if you have risk factors, you should be screening at age 40 because then the benefit is there," says Stephanie Bernik, MD, chief of surgical oncology at Lenox Hill Hospital in New York City.

Bernik says she was relieved to see the new studies because she felt guidelines issued in 2009 that recommended that most women wait until age 50 to start getting regular mammograms were premature and might discourage some younger women who could benefit from the tests.

"This is better than what they said before," says Bernick, who was not involved in the research.

But for some researchers, it's still not enough. Since the research is preliminary and is meant more for policy makers than for individuals, one researcher called it "ivory tower" information that still isn't intended to help a younger woman make a decision.

Refining Recommendations on Mammograms

In 2009, the U.S. Preventive Services Task Force (USPSTF) said that most women should get routine mammograms every two years starting at age 50 instead of age 40.

That recommendation conflicts with guidelines from the American Cancer Society, the National Cancer Institute, and the American College of Radiology, which all recommend screening starting at age 40. And it has drawn mixed reactions from patients and doctors.

Some groups applauded the conservative approach, saying that it would reduce the harms of over-testing and overtreatment, which are greatest for women in their 40s.

Others said it would unnecessarily put women's lives at risk, since cancers found in younger women can be aggressive and early detection of an aggressive cancer may be a woman's best hope for survival.

Ultimately, the USPSTF said the decision to start breast cancer screening before age 50 should be left up to individual women and their doctors.

But until now, there's been little information to help guide that decision.

Family History or Dense Breast Tissue Doubles Risk

The new studies, which were conducted by the same group of researchers that compiled the evidence for the 2009 USPSTF recommendations, are meant to help clarify when mammograms might be useful for younger women.

The first study used four different models to simulate the benefits and harms of screening mammography in women ages 40 to 49.

That study found that women in their 40s need to have double the average risk of getting breast cancer to get the same degree of benefit from regular mammograms, meaning every other year, as women in their 50s.

"Between 40 to 49, the chance of developing breast cancer is under 2%, so even when you double that, it's still low," says researcher Jeanne S. Mandelblatt, MD, MPH, associate director for population sciences at Georgetown University Medical Center's Lombardi Comprehensive Cancer Center in Washington, D.C.

In a companion study, researchers asked what risk factors might actually double a woman's risk for breast cancer in her 40s.

For that study, researchers reanalyzed data from 66 published studies and included data on more than 380,000 women who are being tracked through the Breast Cancer Surveillance Consortium, a network of seven mammography registries.

Out of 13 distinct risk factors identified through the studies and registries, only two fully doubled a woman's risk for breast cancer in her 40s.

"To have a twofold increase in risk, you need to have a first-degree relative -- a mother, daughter, or sister -- with breast cancer. Or you need to have extremely dense breasts. There aren't that many women who have either of those conditions," Mandelblatt says.

For women with more than one first-degree relative with breast cancer, the risks were even higher -- four to 12 times greater than average.

If a first-degree relative was diagnosed before age 40, a woman's risk of breast cancer was three times higher than average.

The issue of breast density is a complicated one, researchers admit, because density can only be determined by first getting a mammogram.

Experts don't recommend that women get a baseline mammogram to discover breast density.

"Mammography density is sort of a newer area," says researcher Heidi D. Nelson, MD, MPH, an investigator at the Oregon Evidence-based Practice Center and the Knight Cancer Institute at Oregon Health & Science University in Portland.

"Radiologists aren't in good agreement about how to read breast density, and we're not sure how to drive that car, yet, really," Nelson says. "So it would be good to maybe wait for more research about exactly how to make decisions with that information."

But Nelson says the study should also comfort women who worry that things like physical inactivity and body weight might put them at increased risk for breast cancer. The study found those had relatively little influence on a person's risk. Other factors that didn't appear to raise risk substantially included race, smoking, and alcohol use.

"What's really reassuring is that there are a lot of risk factors that really don't have a huge increase in risk attached to them," says Nelson.

Understanding Personal Risk

Researchers were also careful to stress that the pair of studies was meant for policy makers, not for individual women to use to try to discern their own risk.

"These data do not present recommendations on what women should or shouldn't do," says Diana Buist, PhD, a senior investigator at Group Health Center for Health Studies in Portland, Ore.

"This should not be used for adding your risk as an individual person," Buist says, adding that it's better to talk through issues of risk with your doctor before deciding on whether to get a mammogram.

"Mammography is not a perfect tool," Buist says. "It just doesn't work as well in younger women. Because it doesn't work as well, it means that there are harms and benefits that are important for women to understand."

Other experts found the studies frustrating because they stopped short of offering any new advice.

"I'm not sure where that leaves women in their 40s who aren't sure what to do," says Kathryn Evers, MD, director of mammography at Fox Chase Cancer Center in Philadelphia. "I think the people who know they have bad family histories know they want mammograms, and it's not a discussion. I think for everybody else it's a very difficult problem."

"Most women who get breast cancer don't have these risk factors. What do you do if you're a 45-year-old woman with kids and you're scared?" Evers says. "It is ivory tower research in a lot of ways, and it's very hard to get a good practical message out of it, for me."

Advice to Women Considering Mammograms

Until there are better screening tools to replace mammography, Evers say there are two things women can do to better use the test.

The first is to find a good doctor who will carefully discuss the benefits and risks.

Studies show that about half of women who get an annual mammogram for 10 years starting at age 40 will have at least one false-positive result that leads to a cancer scare.

The benefits of mammography include early detection. One review suggests that mammograms have reduced breast cancer deaths by 15%.

If you do decide to get tested, Evers says it's smart to seek out a radiologist who is a dedicated mammographer, which means that they only read mammograms.

Mammographers are specialists, and studies show they are more likely to catch cancer when it's there and correctly rule it out if it's not. They're also less likely to order unnecessarily follow-up tests.